The invention relates generally to rolls, and more particular to an improved support and lubricating system for an hydraulically supported roll.
Rolls in which a hollow roll of the type having a rotating hollow roll forming a working roll circumference at its outer diameter and a stationary cross piece extending through the hollow roll forming a clearance space therewith, with the cross piece having ends protruding from the hollow roll to which external forces may be applied and a means including a liquid for hydraulically supporting the hollow roll provided at the cross piece, the hollow roll further having a bearing arranged at each of its ends which rotatably supports the hollow roll and to which lubricant is conducted are known.
A roll of this type with a sealing arrangement located at the cross piece which divides a longitudinal chamber formed between the hollow roll and the cross piece is described in German Patent No. 31 28 140. The seal disclosed therein comprises transverse end seals provided at the opposite ends of the longitudinal chamber as well as longitudinal seals extending along the cross piece and the hollow roll on both sides of the action plane of the roll. This patent shows a seal design for the so-called "floating roll" in which liquid leaking past the transverse end seal lubricates bearings which are arranged outside the transverse end seal to rotatably support the hollow roll on the cross piece. Usually, the liquid is an hydraulic oil which can serve both as the pressure liquid for supporting the hollow roll and the bearing lubricant when the "floating roll" is operated at normal temperatures.
The "floating roll" may also be used as a heated roll in which the pressure liquid is brought to an elevated temperature. The "floating roll" is particularly well suited for heating applications because, even though a large cross section for conducting the heating liquid is provided, good temperature uniformity over the width of the web of material can nevertheless be achieved with suitable control of the stream of liquid. This is accomplished by allowing the pressure liquid in a longitudinal pressure chamber formed adjacent to the rolling gap to flow in one direction along the roll and then in the opposite direction where it is collected in a longitudinal leakage chamber.
However, there are limits to the temperatures that may be achieved in the normal floating roll because the common pressure liquids which have good bearing lubrication properties decompose at higher temperatures. Furthermore, liquids which can withstand higher temperatures do not have sufficient lubricating properties. Therefore, a problem arises when using known rolls as heated rolls because there is a temperature limit which cannot be exceeded due to use of the same liquid for exerting the pressure, supplying the heat and lubricating the bearings.
Other rolls are known in which the pressure liquid used in the hydraulic device to support the hollow roll at the cross piece is also used for lubricating the bearings. In DE-OS No. 24 20 324 the hydraulic device comprises several piston-like pressure elements arranged in the cross piece to act against the inside circumference of the hollow roll in which leakage oil therefrom is used to lubricate the bearings DE-OS No. 29 02 956 shows the provision of additional spray devices which direct hot oil against the inside circumference of the hollow roll.
In order to solve the aforementioned problem and other disadvantages of known rolls, it is a primary object of this invention to provide a hollow roll of the type previously specified in which ambient temperatures of about 240.degree. to 250.degree. C. at the working circumference of the roll can be achieved. This requires the heat carrier liquid in the longitudinal chambers to be maintained at temperatures of 260.degree. to 280.degree. C.
It is a more specific object of this invention to separate the pressure and heat carrier liquid located in the clearance space between the hollow roll and the cross piece from the bearing lubricant by a distance such that no substantial heat transfer occurs between the heat carrier liquid and the lubricant.
Another object of the invention is to minimize heat transfer from the pressure and heat carrier liquid into the cross piece and the bearing rotatably supporting the hollow roll.
It is yet another object of this invention to provide for ready access to the aforementioned bearing without separating the cross piece and hollow roll.
Another object of the invention is to provide an external bearing, upon which the roll is supported in a machine frame or the like, having an outside diameter smaller than the outside diameter of the hollow roll in order to overcome spatial constraints.
It is still another object of this invention to provide a housing means for the bearing which supports the cross piece over a sufficient distance free of play in order to withstand the torque exerted by the housing when the roll is loaded.
It is yet another object of this invention to provide a seal at the end of an extension of the hollow roll which accommodates for misalignment between the extension and cross piece due to deflection of the cross piece when the hollow roll is loaded.
A still further object of this invention is to prevent air from coming into contact with pressure and heat carrier liquid in the vicinity of the aforementioned seal to obviate the build up of an undesirable gummy coating or film which hampers the effectiveness of the seal.
Finally, another object of the invention is to prevent the excessive leakage of pressure and heat carrier liquid from the longitudinal chamber of the hollow roll.